This invention relates generally to a method and apparatus for recording and reproducing an information signal and, more particularly, is directed to a method and apparatus for recording and reproducing a color television signal comprised of a video signal and an audio signal on a magnetic tape with a plurality of rotary magnetic heads.
Information signal recording and reproducing apparatus for recording and reproducing a video signal on a magnetic tape by means of a rotary magnetic head assembly are well known in the art. For example, in a helical scan type video tape recorder (VTR), at least one rotary magnetic head is rotated at a predetermined angle with respect to the longitudinal or tape running direction of a magnetic tape as the latter is advanced so as to form successive video tracks extending obliquely on the magnetic tape. With the helical scan type video tape recorder, it is possible to achieve high density recording of the video signal by advancing the magnetic tape at a slow running speed and, at the same time, providing a high relative speed between the magnetic head assembly and magnetic tape. However, with known helical scan type video tape recorders in which an audio signal is recorded and reproduced on an audio track extending in the longitudinal or tape running direction of the magnetic tape by a stationary magnetic head, there results a deterioration of the signal-to-noise (S/N) ratio and an increase in the wow and flutter when the speed of advancement of the magnetic tape is reduced. This, of course, results in a deterioration in the quality of the reproduced audio signal, causing the audio signal to have unsatisfactory quality when reproduced.
In order to overcome the aforementioned problem in the recording and reproducing of an audio signal by a stationary magnetic head, it has been proposed to effect the recording and reproducing of the audio signal by means of a rotary magnetic head. With this proposal, an overscan section is provided for each oblique track, for example, by increasing the tape winding angle about the guide drum assembly of the helical scan type video tape recorder. In this manner, each record track obliquely formed on the magnetic tape by the rotary magnetic head assembly includes a video track section and an audio track section, the latter of which corresponds to the aformentioned overscan section. The audio signal that is recorded and reproduced with respect to the audio track section of each track is processed as high density data obtained by processing the signal with a time axis or base compression and a time axis or base expansion.
In one known apparatus, two rotary magnetic heads are provided and are spaced apart by 180.degree.. Thus, each head scans alternate ones of the successive tracks extending obliquely on the magnetic tape. It has been proposed to compress the audio signal and record the same in an overscan section at the beginning of each track with such known apparatus. It is to be appreciated, however, that a complete recording of the video signal must be performed before the audio signal is recorded in order to receive the entire audio signal and process the same prior to recording. If the two magnetic heads are designated as the A head and the B head, the timing of the A and B heads is such that, after the A head has completed recording the video signal in a first track, the B head just completes recording of the audio signal at the beginning of the next adjacent track. Thus, the audio signal corresponding to the video signal recorded by the A head must be recorded by the A head during the next scan of a track thereby. This means that the beginning of recording of the audio signal by the A head is delayed from the beginning of recording of the video signal corresponding thereto by approximately two field intervals, that is, one frame interval. As a result, a problem of lip synchronization occurs in which movement of an actor's lips is sufficiently advanced with respect to the sound corresponding to such movement so as to be noticeable.
It has also been proposed to record the audio signal in overscan sections at the end of each track. With this arrangement, after the A head has recorded one field interval of the video signal in a track, the B head records the compressed audio signal corresponding thereto at the trailing end of the next adjacent track. However, since the audio signal is recorded at the trailing end of each track, a delay equal to substantially two field intervals is again produced from the beginning of recording of the video signal by the A head to the time when the B head begins recording the audio signal corresponding thereto in the next adjacent track. As a result, the lip synchronization problem also results with this proposal.